The present invention relates generally to suspension systems for trucks and trailers and, in a preferred embodiment thereof, more particularly provides a suspension system which includes an integrally formed axle seat.
Suspension systems for large trucks and trailers perform many functions related to the comfort, convenience, and safety of transporting such vehicles on a highway surface. Simply stated, a suspension system acts as an interface between a frame or body of a vehicle and a portion of the vehicle which engages a road surface. The suspension system typically supports or "suspends" the frame and/or body above the road-engaging portion, provides compliance which permits relative motion between them, absorbs shock, adjusts for varied loads and road conditions, structurally interconnects various components of the frame and road-engaging portion, etc.
Many types of suspension systems are well known in the art. One of these is known as a fabricated "trailing arm" suspension system. Generally, a trailing arm suspension system incorporates an approximately horizontally disposed arm that is aligned with a direction of travel of a vehicle. A forward end of the arm is usually pivotably attached to a hanger or bracket extending downwardly from the vehicle's frame.
An end of an axle is typically attached to the arm, such that the axle is perpendicular to the arm, and the axle is in most cases rearwardly disposed relative to the hanger. The other end of the axle is likewise attached to another arm. In this manner, the axle is secured to the vehicle and aligned perpendicular to the direction of travel of the vehicle.
A biasing member, such as a spring, is usually connected between the frame and the axle or arm. The spring, thus, biases the frame away from the axle. As a load is added to the vehicle, the spring may compress, or, conversely, as the load is removed from the vehicle, the spring may expand. Where the vehicle is equipped with conventional air springs and leveling valves, the leveling valves automatically adjust air pressure in the air springs so that the springs are maintained at substantially the same heights regardless of the load added to the vehicle. In that case, spring rates of the air springs are varied as the air pressure in the air springs are adjusted by the leveling valves, such that the spring rates increase with increased load added to the vehicle. While the vehicle is being transported across the road surface, the spring may be temporarily compressed as the road-engaging portion strikes an irregularity in the road surface, the spring later expanding when the irregularity has been traversed.
An example of a typical trailing arm suspension system may be found in U.S. Pat. No. 5,116,075 to Pierce, the disclosure of which is hereby incorporated by reference. In the trailing arm suspension system described therein, an air spring is utilized as the biasing member and a complex clamp is used to attach the axle to the arm. However, in addition to the exceedingly complicated axle clamping structure, the Pierce suspension system suffers from a disadvantage in that the axle clamping structure imparts substantial transverse loads to the axle. Most vehicle axles are highly stressed in the first instance and additional loads imparted by an axle clamp may either cause premature failure of the axle or require a stronger, and, thus, heavier, axle to compensate for the additional loads.
Furthermore, axle clamps, such as those utilized in the Pierce trailing arm suspension system, must be periodically checked for tightness. Loose axle clamps are known to cause premature suspension system failure. This periodic maintenance adds to the overall cost of the suspension system to its user.
One type of trailing arm suspension system is known as a "spring beam" suspension system. In a spring beam suspension system, the arm is a relatively flexible elongated member known as a "spring beam". Advantages of a spring beam suspension system include additional vertical compliance afforded by the spring beam and an ability of the spring beam to absorb torsional loads imparted thereto by the axle.
A typical spring beam suspension system is found in U.S. Pat. No. 4,506,910 to Bierens, the disclosure of which is hereby incorporated by reference. An axle is rigidly clamped to two transversely spaced apart spring beams. The axle is longitudinally intermediate hangers suspending forward ends of the spring beams from a vehicle frame, and air springs disposed between rear ends of the spring beams and the frame.
If one opposite end of the axle is vertically displaced relative to the other opposite end of the axle, such as when a wheel attached to one end of the axle traverses an irregularity on the road surface, the axle is effectively rotated about a longitudinal axis of the vehicle. Since the axle is rigidly clamped to the spring beam, such rotation is transferred from the axle to the spring beam, causing the spring beam to torsionally flex. Some of this torsional loading is absorbed by a pivot bushing attached to the forward end of the spring beam.
In trailing arm suspension systems having rigid arms, instead of spring beams as hereinabove described, such torsional flexing is typically absorbed by elastomeric bushings mounted at the pivotable attachments of the arms to the hangers. An example of such bushings may be found in U.S. Pat. No. 4,991,868 to VanDenberg, the disclosure of which is hereby incorporated by reference. The VanDenberg bushings have vertically spaced apart voids formed therein which enable the bushings to have greater compliance in response to the torsional flexing. Some trailing arm suspension systems are bushed both at the front pivot and at the attachment of the axle to the trailing arm, thereby absorbing the torsional flexing in multiple bushings.
Transverse links, which extend generally parallel to the axle and couple the axle directly to the vehicle frame via pivoting bushed connections at each end of the transverse links, are sometimes required to control transverse displacement of the axle relative to the vehicle frame. Such transverse displacement is commonly referred to as "track out" and may occur when, for example, the vehicle negotiates a corner. Transverse links are typically required where the spring beam is not sufficiently rigidly attached to the axle of the suspension system and, thus, add to the installation time, maintenance requirements, and overall cost of such suspension systems.
A disadvantage of each of the above-described suspension systems is that the axle is clamped to the arms or spring beams with complex, maintenance intensive, potentially stress-inducing, and/or unreliable clamping devices. Most of these suspension systems, and others, rely solely on U-clamps to clamp the axle to the arms. Unfortunately, U-clamps are notorious for their tendency to loosen over time. Other clamping devices, such as that described in the patent to Pierce, impart undesirable stresses to the axle.
From the foregoing, it can be seen that it would be quite desirable to provide a suspension system which does not include an axle clamping device that is complex, maintenance intensive, stress-inducing, or unreliable, but which includes an axle seat that effectively and rigidly attaches an axle to the suspension system, is simple and straightforward in design, is economical to manufacture, and that is reliable in operation. It is accordingly an object of the present invention to provide such a suspension system.